Fix docs for aiImportFileExWithProperties. (#5925)

The docs talked about the importer, but no importer exists in the
context of calling this function. It seems like the docs may have been
accidentally copied from somewhere else.
I copied the docs from another import function within the same file.
This seems reasonable because the implementations of both functions
suggest they work the same way: the function creates the importer and
sets it into the scene private data so that the later release call can
release the importer.

Co-authored-by: Kim Kulling <[email protected]>

include/assimp/cimport.h

@@ -170,10 +170,11 @@ ASSIMP_API const C_STRUCT aiScene *aiImportFileExWithProperties(
 // --------------------------------------------------------------------------------
 /** Reads the given file from a given memory buffer,
  *
- * If the call succeeds, the contents of the file are returned as a pointer to an
- * aiScene object. The returned data is intended to be read-only, the importer keeps
- * ownership of the data and will destroy it upon destruction. If the import fails,
- * NULL is returned.
+ * If the call succeeds, the imported data is returned in an aiScene structure.
+ * The data is intended to be read-only, it stays property of the ASSIMP
+ * library and will be stable until aiReleaseImport() is called. After you're
+ * done with it, call aiReleaseImport() to free the resources associated with
+ * this file. If the import fails, NULL is returned.
  * A human-readable error description can be retrieved by calling aiGetErrorString().
  * @param pBuffer Pointer to the file data
  * @param pLength Length of pBuffer, in bytes